(1) Field of the Invention
The present invention relates to a prevention against noise of a digital audio circuit.
(2) Prior Art
Development in the field of digital electronic engineering today has contributed to the popularity of digitization of audio equipment.
In an audio reproducing equipment, a digital audio disk for which signal processing is digitized has been realized including digitization of the control unit.
FIG. 1 is a block diagram showing a configuration of conventional digital audio disk player, wherein an optical deck mechanism 10 comprises a disk motor 11, a light pickup 12 and a feed motor of the light pickup, each of which is controlled by an optical deck control circuit 20. RF signal from the light pickup 12 is reshaped by a pre-amplifier 30 and sent to a digital signal circuit 40.
The digital signal circuit 40 comprises a synchronous detection circuit 41, a digital signal processing circuit 42, and a crystal oscillator 43 working as a clock pulse generating source, an output of digital signal is sent to a digital-analog converter 50 through a digital signal line 44 to have the digital signal converted into an analog signal, separated then into left and right analog signals, and is sent to an analog signal circuit 60 through an analog signal line 51.
The analog signal circuit 60 comprises low-pass filters 61, and an analog signal is output from output terminals 62.
A system control unit 70 comprises an operation key 72, a display 73 and a system control circuit 71.
Then, each unit is packaged in high density in one cabinet to constitute a digital audio disk player.
Meanwhile, a clock pulse signal generated by the crystal oscillator 43 and a current fluctuation due to operation of logical elements constituting the system control circuit 71 and the digital signal processing circuit 42 effect themselves a noise source.
The noises are transferred directly or indirectly to the analog signal circuit 60 through electrostatic and magnetic coupling among the units packaged in high density, thus impairing the standard of an analog signal output.
To cope with the problem mentioned above, a prevention taken hitherto is such that the portion whereas noise is produced and the analog signal circuit 60 are shielded, or a filter is inserted therein to thereby remove the noise.
As a result, a noise component can effectively be retained at a practical level as the analog signal output thereby.
However, such method is still not effective in removing thoroughly an influence of the noise transferred through the analog signal line 51, and thus a satisfactory high analog audio signal output is not obtainable for high fidelity sound reproducing.